"With al-Qaida and Islamic terrorism we're talking about an international movement with thousands of members, which is actively recruiting in the United States and attempting to attack the United States," said King, a Seaford Republican and the panel's chairman.

"Here we have one deranged person who carried out an attack," he said of Anders Behring Breivik, arrested in the deaths of 76 people from a bombing in Oslo and a youth camp shooting spree.

"We are always going to have the isolated madman," King said, adding there's no evidence Breivik is linked to U.S. groups or recruiting here.

Muslim and civil liberties groups and Democrats including the committee's top Democrat, Rep. Bennie Thompson of Mississippi, have urged King to broaden his focus.

"Our position remains the same as the first hearing, which is to look at all forms of violent extremism, regardless of the ideological source," said Alejandro Beutel of the Muslim Public Affairs Council.

Today's hearing -- the third in a series on Muslim radicalization -- will focus on links between the al-Shabab terror group and al-Qaida in Yemen, and the threat that represents, King said. The hearings come after Ahmed Abdulkadir Warsame revealed those terror ties during interrogations on a Navy warship, and Omer Abdi Mohamed pleaded guilty to helping Somali men in Minneapolis join al-Shabab.

Meanwhile, the State Department issued an updated warning on Tuesday to U.S. travelers abroad about the threat of al-Qaida and affiliated organizations around the world.

In a Senate confirmation hearing Tuesday, President Barack Obama's choice to lead the National Counterterrorism Center, Matthew Olsen, said "al-Qaida is weakened" but continues "to pose very significant threat to our country."

Also, Homeland Security and New York Police Department officials told a House hearing that progress is being made in detecting possible "dirty bombs" and other radiological weapons of mass destruction.

But a Government Accountability Office analyst said there are still technological problems with radiation detectors.